1. Field of the Invention
The present invention relates to an image display system capable of viewing an electronic image and an external sight simultaneously, or selectively.
2. Related Art Statement
Hitherto, there has been provided a head mounted display (hereinafter, referred to as an HMD) having for example a see-through function capable of viewing not only an electronic image, but also an external sight (for example, refer to Japanese Patent Application Opened Nos. 281,891/90 and 26,289/92).
For example, Japanese Utility Model Application No. 52,288/94 discloses an image display system in which a plurality of see-through HMDs can be connected to a controller for outputting image signals, a third party other than a viewer can control through the controller one operation mode which renders a given electronic image viewable to all viewers or an other operation mode which renders an external sight viewable to all viewers.
According to such an image display system, there is an advantageous effect that for example, when applying the system as a service for passengers on a passenger airplane, in the case of the taking-off and landing of the airplane, a given electronic image such as "fasten seat belt" can be forcibly viewed, or when applying education, it can be rendered that all persons present at a lecture pay attention to a blackboard forcibly, or it can be rendered that all of them view an electronic image of a given problem forcibly.
The present inventors found that there are points to be improved in the above image display system. That is, in the above image display system, a plurality of HMDs are connected to only one controller, so that the number of HMDs are limited. The controller itself for controlling the image signals also has a function for controlling the operation mode of the HMD forcibly from the outside, so that it is necessary to provide a circuit for generating such a forcible control signal in the controller. However, such forcible control circuits or the like are efficient in the case of using a plurality of HMDs, but these circuits are not necessary in the case of using only one HMD, so that in such only one HMD utilization, the system construction becomes uneconomical.